I realise that this is a bit of a thread revival, but there seems to be a lot of confusion over the usernames and passwords used to access the O2 EDGE service.
To clarify for contract/Simplicity users:
You should be using the APN "mobile.o2.co.uk".
A variety of usernames will work, including "o2wap", "mobileweb", "faster", but there is an important difference with the "faster" username.
When you use the "faster" username, the GPRS network is compressing images and data before being delivered to your handset. The network is not technically operating any faster when using this username, but instead you are receiving compressed data. The compression does, however, reduce the quality of some data types like images (and possibly also audio?).
This might also be true of other usernames that are provided to you by default. To bypass the compression, use the username "bypass" and the data will not be modified before being sent to you.